This invention generally concerns open-end friction spinning, and in particular a spinning method and device in which fibers are twisted together into a yarn alongside a suction slit extending over both a fiber feeding zone and a subsequent twisting zone. The yarn is produced in a spinning nip formed by two friction rollers in close proximity to each other and driven in the same direction. Such yarn is subsequently drawn off from the spinning nip.
It is known in the prior art to feed fibers into a nip, defined between two friction rollers in close proximity to each other and driven in the same direction, where they are twisted together into a yarn and subsequently drawn off in the axial direction of the friction rollers. For example, see German Pat. DE-OS No. 3,340,825. Formation and consolidation of the yarn takes place alongside a yarn-forming line within the nip area. The position of such yarn-forming line within the nip area depends on the diameter of the yarn to be produced.
A feeding channel is provided to convey fibers from an opening cylinder (by which they are opened in a conventional manner) into the nip area. The fibers are fed through such feeding channel either directly into the nip, or onto a casing surface of one of the friction rollers. To obtain the needed air stream both in the feeding channel and for the retention of fibers in the area of the yarn-forming line, at least one of the two friction rollers is perforated. The perforated friction roller thereby defines a suction roller which is subjected to negative air pressure (i.e. suction) over its entire length by means of a suction insert. The suction insert is equipped with a suction slit which extends alongside the yarn-forming line.
Such open-end friction spinning method is thought to be particularly well suited for the production of fine yarns, since rolling of the fiber sliver in the nip between the friction rollers makes it possible to obtain a high degree of twisting and high output speed in a relatively simple manner. However, a drawback has been found that, especially with fine yarns, spinning results did not meet expectations with regard to solidity and output speed.